[hijack]

Check the hl2.exe you installed, it should be 86 088 bytes and sit where steam.exe is installed. Then check that it has properly overwritten the file steamapps/<your account>/half life 2/hl2.exe (it should be the exact same file after you started hl2 via hijacked steam).

Try to run hl2.exe without steam. It should complain about a missing dll. If it says anything else, you probably have a corrupted file.

Here's the md5sum of hl2.exe: b00737498dbb7d4ab17c44aec27d50bd

Edit: Try with torrent link above, it's an updated version